Diabetes is a lifestyle-related disease that has been strongly associated with dietary habits. Specifically, even in Japan, mild cases of type II diabetes mellitus, which account for at least 90% of all diabetic individuals, continue to increase as dietary habits tend more towards meat-based diets. Moreover, as co-existing illnesses with diabetes, serious disorders of various organ systems, such as diabetic retinopathy, diabetic nephropathy, and diabetic neuropathy are known, and in addition thereto risk factors from circulatory disorders, such as arteriosclerosis, or myocardial infarctions may also have a significant impact on the life prognosis of the individual. Thus, whether or not blood glucose level can somehow be controlled on a daily basis is a major factor in determining the life prognosis or future quality of life (QOL) of these individuals.
Among daily diets, indigestible dextrin, wheat albumin, guava tea polyphenol, soy milk extract, L-arabinose, etc., are offered as food products having hyperglycemic inhibiting effects, and commercial food products including these have already been approved for labeling as special health foods. These functional foods have also attracted a lot of interest, since they demonstrate a high degree of safety, without the side effects, etc. as seen in medicaments. Thus, Yacon is offered as a functional material that is distinct from these.
Yacon (Smallanthus sonchifolia) is an Asteraceae plant that is indigenous to the Andes mountains. The present inventors have reported discovering a hyperglycemic inhibitory activity in hot water extract of an aerial part of Yacon, that α-glucosidase inhibitory activity is associated with the onset of such an effect, and that a dicaffeoylquinic acids (DCQAs) within the extract, such as 3,4-dicaffeoylquinic acid, have a strong or selective α-glucosidase inhibitory activity (refer to Non-Patent Document 1). Moreover, it has been reported that a tricaffeoylaltraric acid contained in Yacon shows activity as an anti-oxidative agent (refer to Patent Document 1).
Recently, it has been reported that the onset of diabetes is stimulated by the affects of active oxygen on the pancreatic islets of langerhans, and that these effects are inhibited by the administration of anti-oxidative substances (refer to Non-Patent Documents 2 and 3). Moreover, it has also been reported that blood glucose levels in a streptozotocin (STZ) induced diabetic mouse were decreased via a polyphenol with anti-oxidative activity (refer to Non-Patent Document 4). Caffeic acid and DCQAs are known to have an anti-oxidative activity (refer to Non-Patent Documents 5 and 6).    Patent Document 1: Japanese Patent No. 3039864;    Non-Patent Document 1: Terada S., Ito K., Taka M., Ogose N., Noguchi N., Koide Y, Natural Medicines, 57, 89-94 (2003);    Non-Patent Document 2: Tanaka Y, Gleason C. E., Tran P. O. T, Harmon J. S., Robertson R. P., Proc. Natl. Acad. Sci. U.S.A., 96, 10857-10862 (1999);    Non-Patent Document 3: Katoh M., Sakurai K., Fujimoto Y., YAKUGAKU ZASSHI, 122, 831-839 (2002);    Non-Patent Document 4: Moharram F. A., Marzouk M. S., El-Toumy S. A., Ahmed A. A., Aboutabi E. A., Phytother. Res. 17, 767-773 (2003);    Non-Patent Document 5: Chuda Y., Ono H., Ohnishi-Kameyama M., Nagata T., Tsushida T., J. Agric. Food Chem. 44, 2037-2039 (1996); and    Non-Patent Document 6: Ohnishi M., Morishita H., Toda S., Yase Y., Kido R., Phytochemistry, 47, 1215-1218 (1998).